Charge Photogeneration in Composites of Fluorinated Carbon Nanotubes and Semiconducting Polymer P3HT

Abstract

Spectroscopic and photovoltaic properties of composites of purified and subsequently fluorinated single‐walled carbon nanotubes (F‐SWCNTs) with conjugated polymer poly(3‐hexylthiophene) (P3HT) are tested. Adding cyclohexanone into o‐dichlorobenzene solution of P3HT and F‐SWCNTs significantly affects the composite morphology and promotes P3HT/F‐SWCNT nanofilament formation, as evidenced from atomic force microscopy (AFM) images of spin‐coated composite films. Also, nanofilament formation enhances quenching of P3HT photoluminescence by F‐SWCNTs. The performance of P3HT‐based organic photovoltaics (OPV) devices with separated semiconducting SWCNTs and F‐SWCNTs as the acceptor component of the active layer is comparable. Light‐induced electron paramagnetic resonance (EPR) signal intensity in P3HT/F‐SWCNT composite films and frozen solutions grows with increase in F‐SWCNT content, which is a signature of photoinduced electron transfer. Dramatic change in SWCNT electronic structure upon fluorination is also evidenced by UV–vis– near infra red optical absorption spectra, from which the bandgap of about 1.0 eV is derived for F‐SWCNTs. Overall, the experimental results confirm that fluorination efficiently converts metallic SWCNTs into semiconducting ones, and F‐SWCNTs can be used for as an electron acceptor component in OPV devices, in combination with polymer donors. Presently, the performance of P3HT/F‐SWCNT devices is limited by F‐SWCNT aggregation into bundles, which decreases P3HT/F‐SWCNT interface area.